1. Field of the Invention
The present invention relates to a substrate constituting an ink jet head for recording, printing or the like (hereinafter, referred to typically as "recording") characters, symbols, images or the like (hereinafter, referred to typically as "images") by discharging ink functional liquid or the like (hereinafter, referred to typically as "ink") on a record holding body including a paper sheet, a plastic sheet, a piece of cloth, and an article (hereinafter, referred to typically as "paper"); an ink jet head using the substrate; an ink jet pen including an ink reservoir for reserving ink to be supplied to the ink jet head; and an ink jet apparatus for mounting the ink jet head.
In the present invention, the ink jet pen includes a cartridge form having an ink reservoir integrated with an ink jet head, and it further includes another form in which an ink jet head and an ink jet reservoir are separately prepared and are removably combined with each other. The ink jet pen is removably mounted on a mounting means such as a carriage of an apparatus main body. In the present invention, the ink jet apparatus includes a form integrally or separately provided on information processing equipment such as a word processor or a computer as an output terminal, and it further includes another form used for a copying machine in combination with information reading equipment or the like, a facsimile having an information transmitting/receiving function, a machine for performing textile printing on cloth, and the like.
2. Description of the Related Background Art
An ink jet apparatus has a feature capable of recording a highly precise image at a high speed by discharging ink from a discharge opening as small droplets at a high speed. In particular, an ink jet apparatus of a type, in which an electrothermal converting body is used as an energy generating means for generating energy utilized for discharging ink and ink is discharged by use of a bubble generated in ink by a thermal energy produced by the electrothermal converting body, is excellent in performances such as high precision of image, high speed recording, and reduction in sizes of a head and the apparatus. In recent years, there have been strong demands of markets towards these performances of the ink jet apparatus, and to meet the demands, various attempts have been made to improve the ink jet apparatus.
One of such attempts for improving the ink jet apparatus is disclosed in U.S. Pat. No. 4,458,256. In this reference, as shown in FIG. 11, for example, return portions of electrodes for imparting electric energy to heat generating portions (hereinafter, in some cases, referred to as "heaters") of resistors constituting electrothermal converting bodies are made common as a common lead electrode, and the common lead electrode is provided to lie as a conductive layer under an insulating layer. With this construction, a plurality of heaters can be arranged to be closer to each other as compared with the conventional manner because they are not interrupted by the return portions of the electrodes. Ink passages communicated to discharge openings are provided to correspond to the heaters. Accordingly, a higher density arrangement of the ink passages can be achieved, leading to a higher density arrangement of the discharge openings, thus obtaining a higher precise image. The higher density arrangement of the ink passages also contributes to saving in space, to thereby further reduce the size of the head.
Examined Japanese Utility Model Publication No. HEI 6-28272 also discloses a construction in which a metal layer as a common lead electrode is provided under a heating resistor layer by way of an under-coat layer. As the material of the metal layer, there are mentioned tantalum, molybdenum, tungsten or the like.
The present inventors have examined the above-described ink jet heads, and found that they have undoubtedly various advantages described above, but they present the following problems; namely, the above-described ink jet heads are possibly shortened in service life contrary to the expectation or are possibly reduced in discharge performance during discharge of ink.
With respect to the cause of the above problems, the present inventors have examined, and found the fact that, for the common lead electrode made of aluminum, a stress concentration region having a projecting shape called a "hillock" is possibly formed on the surface of the common lead electrode due to the thermal effect. In particular, the temperature of a portion near the common lead electrode under the heater instantaneously reaches the melting point of a metal material constituting the common lead electrode due to a high heat energy generated by the heater. Such stress concentration in the common lead electrode acts to accelerate the growth of the hillock, or to generate a new hillock. The generation of hillocks is sequentially propagated upwardly by way of various layers, with a result that a projecting portion having a height of, for example about 2 .mu.m is formed on the bubbling surface of the heater. In such a projecting portion on the bubbling surface, a step portion (corner portion) where the film quality is weakened is concentratedly damaged by the effects of a large variation in pressure and thermal stress generated on the bubbling surface (these effect are called "cavitation") due to the repeated bubbling in the ink passage, and finally ink permeates through the step portion and causes electric corrosion, resulting in the disconnection of the resistor. This brings a failure of the ink jet head, and shortens the service lief contrary to the expectation. Moreover, a strain appearing in the form of the projecting portion on the bubbling surface is increased as the hillock is grown, which gradually exerts adverse effect on the bubbling phenomenon; consequently the discharge performance is reduced during discharge of ink.
The results of the examination on the above-described problem also showed the following point as one of the causes, though there have been an unclear phenomenon. In the case where the common lead electrode is made of tantalum, molybdenum, tungsten or the like as in Examined Japanese Utility Model Publication No. HEI 6-28272, since the resistivity of such a metal is relatively large, the heat generated by the metal itself is accumulated in the head in addition to the heat generated by the heater during discharge of ink. By the effect of the heat thus accumulated, it becomes gradually difficult to keep the thermal control and to keep the normal bubbling phenomenon on the bubbling surface. As a result, the discharge performance is dropped during discharge of ink. This problem significantly emerges in the case that the interval between the heaters is shortened for achieving a higher density arrangement and thus the heat becomes easier to be accumulated, or that the ink jet head is driven at a higher speed and thus the heat becomes easier to be accumulated.